At last a fish farm winning the battle against sea lice

An innovative way of collecting and removing sea lice is being developed following a successful trial by Loch Duart Ltd. Loch Duart is keen to share this innovation with any other salmon farmer interested. “Sea lice have been around as long as salmon have existed and will be as long as they continue to,” said Nick Joy, Managing Director, “Loch Duart hopes and aims to work to ensure that salmon have a long future ahead and that sea lice will not be a significant factor affecting the species’ future. Whilst we are not yet at the point where we can say that sea lice are over as an issue, we can say that we have taken a new step in the control of this perennial pest”.

For some time now we have been researching and developing novel methods to counter sea lice. Loch Duart believes that farming based entirely on medicines is not sustainable but also accepts that we have a lot to learn before we can meet this ideal. We must change and we are changing what we do year on year as we learn more. Not only are we changing the fallow patterns of our sites but also the way we handle our salmon and recovering sea lice dislodged during the process.

Our development team led by Sonja Brown, combined with our fish health biologists and engineering team have come up with an innovative way of collecting and removing sea lice dislodged during handling. Several times during the cycle of their life, our salmon are handled to sort them for size, to reduce bullying, to remove maturing salmon (grilse) or to be harvested for the marketplace. The salmon are pumped from the net by a pump with no moving parts. This uses the ‘venturi’ principle which uses water to draw water up a pipe and the fish are drawn up too. One of the side effects of this method of pumping is that sea lice are dislodged as they enter the high pressure flow.

Over the last year the team have developed a filter system which removes even the eggs from the sea lice and traps them so that they can be removed and destroyed. The system had to cope with huge flows of water and microscopic sea lice stages, whilst avoiding slowing up the flow of fish. The
speed of handling and the quick returning of salmon to the water are critical for their welfare. Loch Duart was the first salmon farm to be approved by Freedom Food. Welfare is critical to us and so our methods must meet the highest standards.

“Nothing is that easy,” says Sonja, “but we knew that we had the germ of an idea. There are many ways of filtering but the size of the lice is so small and the volume of water so large that it presents extraordinary problems. An old filter that we had on site provided us with a good starting point. Our engineers then experimented by adapting engines, fittings and pipes to the grading set up.”

“We know from previous use that our pumps cause about 70% of sea lice to detach. Thus if we could catch all of these, both the numbers and the potential future numbers of sea lice would be considerably reduced without recourse to medicines. We feel we are now in a position to say this.”

Due to the success shown in the operation of the prototype filter, Loch Duart are installing further units to allow filtration of harvests and grading at the same time. The engineering team’s aim is also to refine and integrate the pump and filter for a more efficient use of energy in the system as a whole.

Nick Joy commented, “For many years Loch Duart has talked about how to reduce sea lice numbers without the need for medicines. We have now developed one method and this will have significant impact on our sea lice numbers. We are working on other methods and hopefully will be making further announcements in the not too distant future. I want to congratulate all those involved in this development. Our extraordinarily dedicated biologists and engineers combined in the design and development of this system, making this great step forward possible. Maybe one day we will be able to say that medicines for sea lice are obsolete on our farm. If we do it will be down to the dynamic and driven team that work within our company.”